The present invention relates to the control of an internal combustion engine. More specifically, the present invention relates to a global cam sensing system that may be integrated seamlessly with multiple internal combustion engines having a plurality of cylinder configurations.
Integration of vehicle parts, electronic components, and software into automotive vehicles is becoming increasingly important in today""s automotive industry. Traditional methods of vehicle assembly for vehicle parts and components is giving way to flexible modular design and manufacturing techniques.
Presently, automotive companies manufacture a wide range of internal combustion engine (ICE) configurations such as in-line four-cylinder engines, in-line five-cylinder engines, in-line six-cylinder engines, and V-eight engines. As is known in the art of four-cycle ICEs, position and timing between a crankshaft and a camshaft is very important for the application and synchronization of spark and fuel, as the camshaft actuates the intake and exhaust valves of an ICE. A camshaft may be used in an overhead valve (OHV) configuration where the valves are actuated via pushrods, or in an overhead cam (OHC) configuration where the valves are acted on directly by the camshaft. The camshaft is driven by the crankshaft through a 1:2 reduction (i.e., two rotations of the crankshaft equal one rotation of the camshaft) and the camshaft speed is one-half that of the crankshaft. The crankshaft and camshaft position, for engine control purposes, are measured at a small number of fixed points, and the number of such measurements may be determined by the number of cylinders in the ICE.
In today""s engine control systems, crankshaft speed supplied by a crankshaft sensor provides position, timing, and/or speed information to an electronic controller for controlling the application of spark and fuel to the cylinders of an ICE. The position and timing (phase) of a first camshaft controlling exhaust valves for a cylinder and/or a second camshaft controlling intake valves for a cylinder in an overhead cam engine may be controlled relative to the crankshaft (piston position) to reduce emissions and improve fuel economy. Several cam-phasing devices exist in today""s automotive market that require accurate position and timing information provided by a camshaft position sensor. The camshaft position sensor typically includes a variable reluctance or Hall effect sensor positioned to sense the passage of a tooth, tab, and/or slot on a target or data wheel coupled to the camshaft.
The target wheel or data wheel used in present camshaft position sensors has a generally regular distribution of teeth, tabs, and/or slots. In a four cycle ICE, the electronic controller must further differentiate the intake, compression, power, and exhaust strokes since the cylinders will be at the top dead center (TDC) position during the compression and exhaust phases and at the bottom dead center (BDC) position during the intake and power phases. Accordingly, the application of fuel and spark in a typical ICE will not be applied until enough position information has been obtained from the crank or cam sensing systems. Thus, the engine controller must not only determine the TDC and BDC positions of the cylinder but also the state of the engine cycle to control fuel and spark.
Target or data wheels for a camshaft that provide camshaft position may either be common across all engine configurations (i.e., the number of cylinders) or specific for each engine configuration. Target wheels that are designed to be specific to the number of cylinders in the engine provide the optimum data for functions such as control of a camshaft phaser or delivery of fuel/spark in the event of a failure of the crank sensor circuit. These present systems have the disadvantages of requiring different hardware and software for each engine configuration. Target wheels that are common across all engine configurations may provide the advantage of faster engine position information, but lack enough position information for optimum control of a cam phaser and delivery of fuel/spark in the event of a failure of the crankshaft sensor system. It would be advantageous for an automotive company to utilize a single type of generic camshaft sensing system with a single generic target wheel and calibratible software that can be used on a plurality of engine configurations, while still providing for control of cam phasers, and delivery of fuel/spark in the event of a failure of the crank sensor system, and providing the fastest engine position information.
The present invention comprises a new camshaft sensing system common to four cycle internal combustion engines (ICEs), including but not limited to four, five, six, and eight cylinder engines. The cam system, and specifically the sensor and target wheel, provide an output signal with xe2x80x9ceventsxe2x80x9d at a fixed location relative to top dead center (TDC) compression for cylinders of the engine configurations listed above. This is achieved with the minimum number of sensing features possible to reduce the cost, complexity, and control system throughput of the camshaft sensing system, while maximizing functionality and providing quick engine synchronization.
The present invention utilizes an 8xc3x97+s cam with eight binary (state encoded) base periods for engine cam timing functions. Each semi-period or state is bounded by a rising and falling edge that are a fixed angle before TDC for one or more cylinders of all four, five, six, and eight cylinder engine configurations. In the present invention, the edge that corresponds to TDC for cylinder one is common to all engine configurations. In addition to the base periods for engine timing functions, an additional state is added to the system at a location known as the synchronization region or pulse. This state and its bounding edges are used purely to synchronize the engine quickly when the crank position has been determined. The common camshaft sensing system of the present invention can be used on a plurality of engine types with no loss of functionality, as compared to cylinder number specific cam systems or 1xc3x97 cam system of the prior art.
The 8xc3x97+s cam sensing system of the present invention places an edge (electrical signal) at a consistent location prior to TDC for all four, five, six and eight cylinder engine configurations. Through programming and calibration, each engine controller selects which edge numbers it will use for specific cam tasks. These will generally be those edges that fall at a consistent angle prior to TDC for the specific engine configuration. In addition, all engines will use the xc2xd period known as the sync pulse, and the corresponding opposite state of the cam signal 360 crank degrees later to achieve the full engine sync as quickly as possible. The combination of these properties is unique to this cam sensing system and provides the ability to do all known cam tasks with the highest degree of accuracy using a single common cam system.
The camshaft sensing system of the present invention provides cost, assembly, and integration benefits, as compared to existing cylinder specific cam systems. In addition, the camshaft sensing system of the present invention provides increased functionality over existing systems by providing engine cycle position and timing, cylinder event based cam control (for cam phaser applications), and a backup speed and position signal for spark and fuel control in the event of a failure of the crankshaft sensor.